1. Field of the Invention:
The present invention relates to an indicator of light coverage angle of a photographic flash capable of changing the light coverage angle.
2. Description of the Prior Art
Hitherto in a photographic flash capable of changing angle of the flash light, a means to indicate light angle is provided by being linked with movement of its slidable front lens part. Such prior art is disclosed for instance in the United States Patent Application Ser. No. 925,629.
One example of such prior art configuration is elucidated with reference to FIG. 1(A), FIG. 1(B), FIG. 2(A) and FIG. 2(B).
In FIG. 1(A) which is a plan view of the prior art device, FIG. 1(B) which is a sectional elevation view taken at the sectional plane b--b shown in FIG. 1(A) and FIG. 2(A) and FIG. 2(B) which are plan views, the main body 1 contains flash lamp part 3 comprising a gas discharge lamp 31 and a reflector 32 and printed circuit part 101 which contains electric circuit components 104 constituting known photo-flash circuit. A slidable front lens part 2 having a Fresnel lens 4 is slidably provided on the front hood 102 of the main body 1. The slidable front lens part 2 has, in unitary extended relation, a mask plate 9 having three small windows 5, 6 and 7. The mask plate 9 is slidably inserted under the top cover plate 103, which has a large window 11. Under the mask plate 9 is further provided a fixed plate 105, on the upper face of which letters W, N, and T, corresponding to the setting for a wide angle, normal angle and telephoto angle, are printed.
Operation of the prior art device of FIG. 1(A), FIG. 1(B), FIG. 2(A) and FIG. 2(B) is as follows: By sliding in or out the slidable front lens part 2, the angle of the flash light coverage is changed from wide angle to telephoto angle. When the front lens part 2 is in the most pushed-in position, as shown in FIG. 1(A), the small window 5 lies on the letter W of the fixed plate 105 thereby showing the letter W therethrough. Then, by drawing out the slidable front lens part 2 to the state shown in FIG. 2(A), the next small window 6 comes on the next letter N of the fixed plate 105 thereby showing the letter N therethrough. Lastly, when the slidable front lens part 2 is further drawn out to the state shown in FIG. 2(B), the last small window 7 comes on the letter T thereby showing the letter T therethrough. Thus, by selecting the positions of the letters W, N or T being shown through the windows 5, 6 or 7, coverage angle of the flash light is selected to be wide, normal or telephoto, respectively,
In such prior art device, there is a shortcoming that the mask plate 9 should have a considerable length 1.sub.1 which is larger than the distance 1.sub.2 +1.sub.3 +1.sub.4, which is sum of pitch between the windows 5 and 6, pitch between the windows 6 and 7 and width of a window, respectively. Hence, the length of the mask plate 9 becomes considerably longer than the sliding stroke of the slidable front lens part 2. Accordingly, in order to receive the mask plate 9, the size of the main part 1 necessarily becomes large.
In the prior art apparatus of FIG. 1(A), FIG. 1(B), FIG. 2(A) and FIG. 2(B), there would be a modification wherein the order of the arrangement of the letters W, N and T be inversed. However, such modified apparatus resultantly requires larger size than the prior art apparatus.